Hopes are high in the music sector that Apple will have all the licenses it needs to launch a cloud music service in time for the company's Worldwide Developers Conference, which starts on June 6.

Negotiations between Apple and music publishers have begun in earnest only recently but the amount of money that separates the two sides from reaching a deal is relatively small, according to two sources with knowledge of the talks. That said, these are cloud-licensing contracts, which are new and complex and there are still several ways Apple's service could be delayed, insiders say.

Apple has wrapped up licensing agreements with three of the four top record companies, including EMI Music, Warner Music, and Sony Music. CNET reported last week that Apple and Universal Music, the largest of the major record companies, could ink a deal possibly this week. This would give Apple recorded-music rights to most of the popular music out there. To offer a fully functional cloud music service though, Apple still needs publishing rights.